Light reflected from a dashboard that reflects off a windshield can interfere with a driver's vision. Referring to FIG. 1, veiling glare in a windshield of a vehicle V occurs when ambient light passes through the windshield W, reflects off the upper surface of dashboard D, back onto the windshield W and reflects off the windshield W (shown in broken line) into the driver's eyes. The driver sees a virtual image of the lit dashboard D beyond the windshield W that “veils” or impedes the ability to discern the scene ahead of the vehicle. Veiling glare is exacerbated by windshields having a steep slope (such as in cab forward designs) and light-colored or glossy finished dashboards.
In order to compensate for veiling glare, vehicle manufacturers have been forced to limit the degree of windshield slope, as well as to use dark colors and/or a textured surface on the dashboard. These features limit the options for design of vehicles, and the dark colored dashboards absorb radiation resulting in increased heat within the vehicle. Other systems for reducing veiling glare have focused on the windshield, such as by placing holographic material on the windshield, which is complicated and expensive to manufacture. More recently, veiling glare has been reduced using light polarizing systems.
In one such system, as described in U.S. Pat. No. 6,299,131, a first polarization layer is placed on the interior or exterior surface of the windshield, and a second polarization layer is placed on the dashboard upper surface. The windshield polarization layer and the dashboard polarization layer polarize light in different directions from each other. The described use of a polarizing layer on the surface of the windshield to polarize light transmitted through the windshield in a first predetermined direction is undesirable, as the effective polarization of visible light reduces the transmission of light through the windshield to approximately one-half the original transmission level. This significant attenuation of light transmission can impair the visual ability of a vehicle operator during low light conditions such as at night. Legislation dictates the minimum level of transmission for driver safety. For example, in the United States, the Federal Department of Transportation specifies a minimum of 70% visible light transmission (VLT) for window tinting on the windshield and the windows to the immediate left and right of the driver. Automobile manufacturers and distributors operating in the United States are required by federal law to provide glass with a minimum of 70% visible light transmission. The attenuation of approximately 50% of the original visible light transmission by the described polarization layer on the windshield would not meet the federal requirements.